FISHERY BULLETIN: VOL. 82, NO. 1 



MATERIALS AND METHODS 



The Particle Counter 



The in situ particle counter system was built and 

 described by Mohus (1981), Eriksen (1981), and 

 Eriksen and Mohus (1981). It is presented 

 schematically in Figure 1. The system is based on a 

 Hiac PC-320 Particle Counter 2 which works on the 

 principle of light blockage. The sensor (E-2500, 

 dynamic range 80-2500 ^.m) is installed in a 

 pressure-proof box together with a depth detector. A 

 pump is connected to the sensor, and the sensor and 

 pump are mounted to a rig which is lowered into the 

 sea by winch. Seawater is pumped through a 60 cm 

 long by 2.5 cm diameter hose through the sensor 

 orifice (3 mm), at a flow rate of 6.15 1/min. Particles 

 are counted by the Hiac PC-320 Particle Counter 

 and depth is monitored by the depth detector unit. 

 The "Micro -count" datalogger unit contains an 



Reference to trade names does not imply endorsement by the 

 National Marine Fisheries Service, NOAA. 



input-output interface to accomodate incoming data, 

 a large internal data storage area, operator com- 

 munication via a small CRT display, a keyboard, and 

 a microprocessor with program to control the system. 

 The microcomputer samples data from the Hiac PC- 

 320 Particle Counter and the data sample time can 

 be selected from 1 to 99 s. Finally, a Silent 733 ter- 

 minal is connected to the microcomputer. This ter- 

 minal contains a full text keyboard and a page printer 

 used for initial operator communication and printout 

 of data tables. Two cassette tape stations are 

 included in the terminal. 



The system operates from the surface to 50 m 

 depth, and the registration of particles is presented 

 on the TV monitor as the sensors are lowered into the 

 sea. The vertical distribution of particles can be pre- 

 sented on the monitor at 1, 2 , or 5 m depth, depend- 

 ing on the selected depth intervals. Data are, 

 however, printed out in 1 m depth intervals from the 

 surface to 50 m depth as concentration of particles 

 per liter in six different size groups (150-600 ju.m) on 

 the Silent 733 terminal immediately after the sam- 

 ples have been made. An in situ particle profile is 



I! TEST 

 11 BOX 



Cr - 



i 



DEPTH 

 DETECTOR 



i 



V 



I 



I 



HIAC PC-320 



PARTICLE 



COUNTER 



" ^ JL ^ - 



SENSORS 



INPUT-OUTPUT 



MICRO 

 PROCE- 

 SSOR 



DATA 



STOR- 

 AGE 



COMMUNICATION 



Figure 1.— The particle counter system. 



 



l_ 



SILENT-733 



CASSETTE 

 TAPE 



KEYBOARD-PRINTER 



MICRO-COUNT 



142 



